Hyaline membrane disease (HMD) continues to be a leading cause of mortality and morbidity in prematurely born infants. A most significant impact on mortality data has been made by the antenatal use of glucocorticoid given to the mother to induce pulmonary surfactant production in the fetus in utero. Glucocorticoid treatment can reduce the incidence of HMD from around 20% to 7-10%. Despite treatment, a sizeable proportion of these infants develop respiratory problems. Glucocorticoid treatment is most effective near the time of normal onset of surfactant production. The steroid loses effect on the poorly differentiated lung of the immature fetus. Our preliminary data obtained in the hypophysectomized lamb fetus, suggests that glucocorticoid treatment may also be ineffective in some conditions in which lung development is delayed. The cause of delayed maturation in these fetuses in unknown but one possibility is that normal production of fetal adrenal secretions are required to regulate lung growth. The overall objective of this study is to define the role of adrenal secretions in lung maturation in the ovine fetus. The hypothesis to be tested is that an intact fetal adrenal gland is not only required for normal lung development but is necessary also for premature enhancement of surfactant production caused by pituitary adrenal secretions. The condition chosen for study is the developing lung in the adrenalectomized fetus. The specific objectives are: 1. To detemine cytological, biochemical and functional indices in fetal lung development in these fetuses. 2. To determine whether cortisol, or adrenalin or ACTH administration to these fetuses at Day 128 of gestation, 58 days post-ablative surgery will a) advance histological maturity of the lung; b) change lipid and phosopholipid production; c) advance maturation of lung compliance; d) change the level of pulmonary receptors and of some circulating hormones known to affect lung maturation. The results of the study will identify more precisely the role of the fetal adrenal gland in lung maturation. Information gained from this study will be used to enhance the efficacy of glucocorticoid treatment and further reduce the incidence of HMD.